1. Field of the Invention
This invention relates to a refrigerator oil and a fluid composition for a refrigerator, and in particular to a refrigerator oil and a fluid composition containing said oil for use in a refrigerator, the refrigerator oil comprising an alkyl benzene having a specific feature and being suited for use with an HFC refrigerant containing 1,1,1,2-tetrafluoroethane (HFC-134a) and/or pentafluoroethane (HFC-125).
2. Prior Art
Due to the recent problems as to the destruction of the ozone layer, the use of CFC (chlorofluorocarbon) and HCFC (hydrochlorofluorocarbon) which have been conventionally used as a refrigerant for a refrigerator is now restricted under a regulation. Therefore, as a replacement of these materials, HFC (hydrofluorocarbon) has been increasingly employed as a refrigerant.
Under the circumstances, PAG (polyalkyleneglycol) and esters which are compatible with HFC have been studied or used as an oil for a refrigerator using an HFC refrigerant. For example, the use of PAG is proposed in U.S. Pat. No. 4,755.316; Japanese Patent Unexamined Publications No. Hei 1-198694, No. Hei 1-256594, No. Hei 1-259093, No. Hei 1-259094, No. Hei 1-259095, No. Hei 1-274191, No. Hei 2-43290, No. Hei 2-55791 and No. Hei 2-84491. The use of esters is proposed in PCT. Publication No. Hei 3-505602; Japanese Patent Unexamined Publications No. Hei 3-88892, No. Hei 2-128991, No. Hei 3-128992, No. Hei 3-200895, No. Hei 3-227397, No. Hei 4-20597, No. Hei 4-72390, No. Hei 4-218592 and No. Hei 4-249593.
However, PAG is rather high in hygroscopicity and poor in electric characteristics (volume resistivity). On the other hand, ester-based oils are readily hydrolyzed to generate an acid thus possibly giving rise to various problems. Moreover, these oils are accompanied with a serious problem that they are inferior in lubricity as compared with a mineral oil/CFC or a mineral oil/HCFC.
On the other hand, Japanese Patent Unexamined Publications No. Hei 5-157379 describes a refrigerating system for an HFC-134a refrigerant wherein there is used a refrigerator oil which is incompatible with a refrigerant. As an example of such an oil, an alkylbenzene is disclosed therein. However, it has been found that if an ordinary alkylbenzene is to be used as a refrigerator oil for HFC-134a and/or HFC-125, some specific means is required to be taken on the side of the system, and that if an ordinary alkylbenzene is used as a refrigerator oil for HFC-134a and/or HFC-125 without taking such specific means, the seizure of a refrigerating compressor used may possibly be caused after a long period of its operation.
The present inventors took notice of an alkylbenzene which is free from hydrolysis and hygroscopicity and made an extensive study to finally find out that if an alkylbenzene having a specific property is used as a refrigerator oil for HFC-134a and/or HFC-125, the seizure of the refrigerating compressor can be avoided, thus indicating an excellent lubricity of the alkylbenzene, and that the alkylbenzene is capable of maintaining a high reliability for a long period of time. This invention has thus been accomplished in one aspect.
It has further been found out by the present inventors that when a phosphoric ester compound is added in a specific ratio to the above alkylbenzene having a specific property and the resulting mixture is used as a refrigerator oil in a refrigerator, the wear resistance and load resistance of the refrigerator can be improved. This invention has thus been accomplished in another aspect.